[When you are dividing or multiplying, the number of significant digits in the answer depends on the part of the question with the least significant digits. For example, There are 2.3 miles left for me to walk. but I can only do 1.54 miles. In the answer I will put two significant digits because the least was 2.3 which has 2 significant digits.]
#1 The answer is 4.821. but since the least # of significant digit is 1.5 which has 2. SO the Ans would be 4.8 mm^2.
#2 Ans is 2.7404 but the correct answer would be 3. because 5 has least value of significant digit. But why is 3? Because the number after 2 is greater than 7.
I hope that helps!